The present invention relates to an aluminum alloy member and a manufacturing method thereof and, more particularly, to a piston for an internal combustion engine a manufacturing method thereof.
There is conventionally known a piston for an internal combustion engine, which has a piston body made of an aluminum alloy material. It is common practice to anodize a top ring groove of the piston (in which a top ring is fitted) and thereby form an anodic oxide film on a surface of the top ring groove for improvements in wear resistance and corrosion resistance. This type of aluminum alloy piston faces a technical problem that there occur clearances between the anodic oxide film and silicon particles contained in the aluminum alloy material due to the growth and expansion of the anodic oxide film.
As a solution to such a problem, Japanese Laid-Open Patent Publication No. 2010-90427 proposes a technique for reinforcing an anodic oxide film on an aluminum alloy material by, after the formation of the anodic oxide film, immersing the anodic oxide film in an aqueous solution containing magnesium ions, ammonium ions and fluoride ions for a predetermined time and thereby allowing a compound containing magnesium and fluorine to be deposited in clearances between the anodic oxide film and silicon particles contained in the aluminum alloy material.